JP3876518B2 - Nitride semiconductor substrate manufacturing method and nitride semiconductor substrate - Google Patents

Description

[0001]
[Industrial application fields]
The present invention comprises a nitride semiconductor (In_XAl_YGa_1-XYN, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) The present invention relates to a substrate manufacturing method and a nitride semiconductor substrate.
[0002]
[Prior art]
In general, when a semiconductor is grown on a substrate, it is known that if a substrate lattice-matched with the semiconductor to be grown is used, the crystal defects of the semiconductor are reduced and the crystallinity is improved. However, nitride semiconductors are generally grown on heterogeneous substrates that do not lattice match with nitride semiconductors such as sapphire, spinel, and silicon carbide because there is no lattice-matched substrate in the world.
[0003]
On the other hand, attempts to fabricate a GaN bulk crystal that is lattice-matched with a nitride semiconductor have been made by various research institutions, but only a few millimeters have been reported so far. Is far away.
[0004]
As a technique for producing a GaN substrate, for example, in JP-A-7-202265 and JP-A-7-165498, a buffer layer made of ZnO is formed on a sapphire substrate, and a nitride semiconductor is formed on the buffer layer. A technique for dissolving and removing the buffer layer after growth is described. However, the crystallinity of the ZnO buffer layer grown on the sapphire substrate is poor, and even if a nitride semiconductor is grown as a thick film on the buffer layer, the crystal defect of the entire crystal is 10⁸Pieces / cm²For the above reasons, it is difficult to obtain a good quality nitride semiconductor crystal. Furthermore, it is difficult to continuously grow a nitride semiconductor having a thick film as a substrate on a buffer layer made of thin ZnO.
[0005]
[Problems to be solved by the invention]
When producing a nitride semiconductor element used for various electronic devices such as LED elements, LD elements, light receiving elements, etc., if a nitride semiconductor substrate can be produced, a new nitride semiconductor is formed on the substrate. Thus, nitride semiconductors with few lattice defects can be grown, so that the crystallinity of these elements is dramatically improved, and elements that have not been realized can be realized. Accordingly, an object of the present invention is to provide a method for manufacturing a nitride semiconductor substrate having good crystallinity and a nitride semiconductor substrate.
[0006]
[Means for Solving the Problems]
In the method for manufacturing a nitride semiconductor substrate according to the present invention, a base layer made of a first nitride semiconductor is first grown on a heterogeneous substrate made of a material different from the nitride semiconductor, and a nitride is formed on the surface of the base layer. A first step of partially forming a protective film having a property that the semiconductor does not grow or is difficult to grow, and after the first step, a metal organic vapor phase epitaxy (hereinafter referred to as MOVPE) ) To grow the second nitride semiconductor from the underlayer to the upper portion of the protective film.And forming a cavity at substantially the center of the protective film.After the second step and the second step, the second nitride semiconductor layer is formed on the second nitride semiconductor layer by hydride vapor phase epitaxy (hereinafter referred to as HVPE). And a third step of growing the third nitride semiconductor with a thicker film thickness.
[0007]
The second nitride semiconductor layer is grown in a shape in which the end face is substantially perpendicular to the horizontal plane of the protective film. The second nitride semiconductor layer is grown by adjusting the molar ratio of nitrogen source gas (nitrogen source / group 3 source) to 2000 or less.In at least one of the second step and the third step, the nitride semiconductor is doped with an n-type impurity. As an n-type impurity to be doped, a group IV element such as Si, Ge, Sn, or S is used, and preferably Si or Sn is doped.
[0008]
The n-type impurity in the nitride semiconductor layer is provided with a concentration gradient in at least one of the second step and the third step. The concentration gradient means that the n-type impurity concentration has an inclination, and the inclination may be continuously provided, or the inclination may be provided stepwise.
[0009]
Furthermore, the concentration gradient is adjusted so that the n-type impurity concentration decreases as the distance from the different substrate increases. This is because if the n-type impurity concentration is reduced as it approaches the main surface, the n-type impurity is doped at a high concentration no matter which nitride semiconductor substrate is exposed when an n-electrode is provided later. This is because the second and third nitride semiconductor layer sides can be used as contact layers, which is desirable for reducing the Vf of the device and improving the output. Further, even if etching is performed from the side of the semiconductor layer grown on the nitride semiconductor substrate and an electrode is provided on the etched surface, the second nitride semiconductor layer doped with n-type impurities at a high concentration or the third nitride For the same reason, it is desirable that the physical semiconductor layer be an electrode forming layer.
[0010]
The present invention includes a fourth step of removing at least the heterogeneous substrate, the base layer, and the protective film after the third nitride semiconductor growth. By performing this step, a nitride semiconductor substrate alone, that is, a wafer for stacking semiconductor layers can be obtained. When a semiconductor is grown on the surface of the substrate using this substrate, a semiconductor layer with good crystallinity can be stacked and grown because the third nitride semiconductor layer surface side has fewer crystal defects.
[0011]
The nitride semiconductor substrate of the present invention is a nitride semiconductor substrate having a first main surface and a second main surface grown by a hydride vapor phase growth method, wherein the first main surface or the first main surface The crystal defects near the main surface of 2 are 1 × 10^FivePieces / cm²IsThe nitride semiconductor substrate contains an n-type impurity, and the n-type impurity has a concentration gradient in the nitride semiconductor substrate.It is characterized by that. In order to reduce the crystal defects of the semiconductor layer to be subsequently grown on the main surface, preferably 5 × 10^FourPieces / cm²The following is more desirably 1 × 10^FourPieces / cm²Below, most desirably 1 × 10^ThreePieces / cm²A nitride semiconductor substrate having crystal defects in the vicinity of the following main surface is selected. The vicinity of the main surface is within 5 μm from the main surface, and the number of crystal defects within 5 μm can be measured with a TEM (transmission electron microscope). The crystal defect is observed by a plan-view with TEM and indicates the average defect density.
[0012]
Furthermore, the nitride semiconductor substrate of the present invention is doped with n-type impurities. Preferably, the n-type impurity has a concentration gradient in the nitride semiconductor substrate, and more preferably, as the n-type impurity approaches either one of the first main surface and the second main surface of the nitride semiconductor substrate, n It is desirable to make the type impurity concentration small.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 to FIG. 5 are schematic cross-sectional views showing the structure of a nitride semiconductor substrate for sequentially explaining each step of the manufacturing method of the present invention. In the figure, the thin line shown inside the nitride semiconductor layer schematically shows the direction and number of crystal defects. As shown in FIG. 1, in the first step, a base layer 2 made of a first nitride semiconductor is first grown on a heterogeneous substrate 1, and no nitride semiconductor grows on the surface of the base layer 2. Alternatively, a protective film having a property that hardly grows is partially formed.
[0014]
The heterogeneous substrate 1 may be any substrate as long as it is made of a material different from that of the nitride semiconductor.₂O_Four) Such as an insulating substrate, SiC (including 6H, 4H, 3C), ZnS, ZnO, GaAs, Si, and an oxide substrate lattice-matched with a nitride semiconductor, etc. Substrate material can be used. Further, a substrate in which the main surface of the substrate material is off-angled can also be used.
[0015]
The growth method of the underlayer 2 is not particularly limited, and can be grown by a conventional method known for growing a nitride semiconductor such as MOVPE, MBE, HVPE or the like. Since this underlayer 2 is made of a material different from that of the heterogeneous substrate 1, it has a large number of crystal defects.⁸Pieces / cm²Because of the above, it is not a nitride semiconductor substrate. Most preferably, undoped GaN is grown on the underlayer.
[0016]
As the material of the protective film 10, a material having a property that the nitride semiconductor does not grow or is difficult to grow on the surface of the protective film is selected._X), Silicon nitride (Si_XN_Y), Titanium oxide (TiO_X), Zirconium oxide (ZrO)_XIn addition to oxides and nitrides such as), and multilayer films thereof, metals having a melting point of 1200 ° C. or higher can be used. These protective film materials can withstand the nitride semiconductor growth temperature of 600 ° C. to 1100 ° C., and the nitride semiconductor does not grow or hardly grow on the surface thereof. In order to form the protective film partially (= selectively), for example, a photomask having a predetermined shape is produced by using a photolithography technique, and the material is formed into a gas phase through the photomask. By doing so, a protective film having a predetermined shape can be formed. The shape of the protective film 10 is not particularly limited. For example, the protective film 10 can be formed in the shape of dots, stripes, and a grid surface, and is preferably formed in a stripe shape. FIG. 1 shows a partial cross-sectional view when a stripe-shaped protective film is formed on the underlayer 2 and the wafer is cut in a direction perpendicular to the stripe. In particular, as shown in FIG. 1, if the area of the exposed portion (window) of the protective film 10 formed partially is smaller than the area of the protective film, the number of crystal defects dislocation from the underlying layer is reduced, and the crystal This is particularly desirable because a nitride semiconductor substrate with few defects can be grown.
[0017]
When the protective film 10 is formed in a stripe shape, the width of the window is adjusted to 10 μm or less, more preferably 5 μm or less, and most preferably 3 μm or less. When the width is larger than 10 μm, the number of crystal defects grown on the protective film tends to increase. Furthermore, in order to obtain a nitride semiconductor substrate with few crystal defects, the ratio Ws / Ww of the width (Ww) of the window portion and the width (Ws) of the protective film is preferably greater than 1 and not more than 20. Preferably it is 10 or less.
[0018]
Next, in the second step of the present invention, MOVPE is used to grow the second nitride semiconductor 3 from the base layer to the top of the protective film as shown in FIG. The second nitride semiconductor 3 is most preferably grown from undoped GaN or GaN doped with n-type impurities in order to obtain a nitride semiconductor with few crystal defects.
[0019]
As shown in FIG. 2, when the second nitride semiconductor 3 is grown on the underlayer 2 on which the protective film 10 is formed, the nitride semiconductor does not grow on the protective film 10, and the window portion The second nitride semiconductor 3 is first selectively grown on the underlayer. As the growth continues, the second nitride semiconductor grows laterally on the protective film 10. A nitride semiconductor that grows in the horizontal direction is different from a nitride semiconductor that grows in the vertical direction like an underlayer, so that the crystal defects are covered with the protective film 10, so that the crystal defects do not dislocation. Crystal defects extend in the lateral direction at the top of the protective film, but tend to stop halfway. Further, although there are crystal defects that dislocation from the window portion appear on the surface of the second nitride semiconductor layer, they tend to stop on the way. If this step is performed by HVPE, the number of crystal defects in the second nitride semiconductor layer tends to increase. This is not preferable in the present invention.
[0020]
In the method of the present invention, as a specific means for growing the second nitride semiconductor layer in the lateral direction substantially perpendicular to the plane of the protective film on the surface of the protective film 10 as shown in FIG. When the nitride semiconductor is grown, it is desirable to adjust the molar ratio of the nitrogen source gas to the group 3 source gas (nitrogen source / group 3 source) to 2000 or less. The preferred molar ratio is adjusted to 1800 or less, more desirably 1500 or less. The lower limit is not particularly limited as long as it is greater than or equal to the stoichiometric ratio, but is desirably adjusted to 10 or more, more preferably 30 or more, and most preferably 50 or more. If the molar ratio is larger than 2000, a triangular nitride semiconductor grows from the window and the crystal defects grow accordingly. Therefore, the crystal defects are less likely to stop halfway, and the number of crystal defects is small. Become more. However, when the gas flow rate is adjusted in this way, a nitride semiconductor grows perpendicularly to the horizontal surface of the protective film, and the vertical surface becomes like a wall and is connected on the protective film. Crystal defects tend to stop during the growth. In addition, crystal defects extending from the window portion tend to stop on the way. Therefore, the second nitride semiconductor layer with few crystal defects can be grown. As shown in FIGS. 3 and 4, the triangular cavity at the substantially central portion of the protective film is a trace of the second nitride semiconductor layer extending and connected perpendicular to the lateral direction.
[0021]
When growing by the MOVPE method, a hydride gas such as ammonia or hydrazine is used as a nitrogen source gas, and an organic Ga gas such as TMG (trimethyl gallium) or TEG (triethyl gallium) is used as a group 3 source gas. Organic Al and organic In gas such as TMA and TMI are used.
[0022]
Further, the n-type impurities such as Si and Sn can be doped during the growth of the second nitride semiconductor layer. n-type impurity concentration is 5 × 10¹⁶/cm^Three~ 5x10^{twenty one}/cm^ThreeIt is desirable to dope in the range of. 5 × 10¹⁶/cm^ThreeIf less, the carrier concentration of the second nitride semiconductor layer becomes insufficient, and the resistivity tends to increase. 5 × 10^{twenty one}/cm^ThreeIf it is more than 1, the impurity concentration is high, so that the crystallinity is deteriorated and crystal defects tend to increase. The preferred range is 1 × 10¹⁷/cm^Three~ 1x10²⁰/cm^ThreeIt is.
[0023]
Furthermore, when the second nitride semiconductor is doped with n-type impurities, it is desirable to provide a concentration gradient in the n-type impurities. In particular, it is desirable that the concentration gradient is adjusted so that the n-type impurity concentration decreases as the distance from the dissimilar substrate increases. This is because the heterogeneous substrate, the base layer, and the protective film are removed, and when the n-electrode is provided on the second nitride semiconductor layer, whatever surface is exposed, the surface is compared with other portions. Since the n-type impurity layer is highly doped, the structure becomes n +, n, and when, for example, a light emitting device structure is stacked on a nitride semiconductor substrate, the Vf of the light emitting device is lowered and the output is improved. .
[0024]
Next, as shown in FIG. 3, when the growth of the second nitride semiconductor layer 3 is continued, the second nitride semiconductor layers that grow laterally on the protective film are connected and integrated. The second nitride semiconductor is a nitride semiconductor substrate having crystal defects that are one digit or more smaller than the above-described underlayer. However, since the film thickness is smaller than that of the base layer, it becomes a substrate in a state where a heterogeneous substrate is attached. However, if the heterogeneous substrate is removed, the second nitride semiconductor tends to be broken apart and hardly become a substrate.
[0025]
The growth thickness of the second nitride semiconductor layer is 1 μm or more, preferably 5 μm or more, and most preferably 10 μm or more, although it depends on the formation width of the protective film 10. This is a film thickness range for covering the upper portion of the protective film with the second nitride semiconductor layer. When the thickness is less than 1 μm, the second nitride semiconductor layer grows laterally on the protective film. Since it tends to be difficult, the number of crystal defects in the third nitride semiconductor layer grown on the second nitride semiconductor layer tends to increase. It is difficult to reduce crystal defects unless it grows laterally. The upper limit is not particularly limited, but is preferably 70 μm or less. If the growth is thicker than 70 μm, the growth time becomes long, the surface of the nitride semiconductor layer becomes rough, and the protective film tends to be decomposed, which is not preferable.
[0026]
Next, in the third step, the third nitride semiconductor 4 is grown on the second nitride semiconductor layer 3 by HVPE with a thickness greater than that of the second nitride semiconductor layer. FIG. 4 shows the state after growth. When GaN is grown as a thick film by MOVPE, the GaN surface tends to become rough. This is because the surface is roughened due to distortion with a different type of substrate due to growth for a long time. If the film is grown for a long time, a protective film (for example, SiO 2₂) Tends to decompose, and pits tend to appear in the nitride semiconductor grown on the protective film. On the other hand, in HVPE, since the growth rate is several times faster than MOVPE, for example, 300 μm can be grown in several hours. For this reason, the third nitride semiconductor having a uniform surface can be grown because it is difficult to be affected by the distortion of the different type substrate and the decomposition of the protective film can be suppressed. In the third step of the present invention, it is desirable that the second nitride semiconductor layer 3 shown in FIG. 3 is grown on the entire upper portion of the protective film and then grown on the second nitride semiconductor layer. However, as shown in FIG. 2, the third step can be performed even when the second nitride semiconductor layer is partially covered with the protective film, and is within the scope of the claims of the present invention. .
[0027]
In HVPE, HCl gas is allowed to flow through Ga metal, while ammonia gas is allowed to flow through another gas pipe, and these gases are mixed on the substrate.
GaCl + NH_Three→ GaN + HCl + H₂
The following reaction takes place. When the third nitride semiconductor is grown as a thick film by HVPE on the second nitride semiconductor with few crystal defects in this way, there are almost no crystal defects extending in the vertical direction, and the entire crystal defects are very large. Less nitride semiconductor can be grown. The third nitride semiconductor layer has fewer crystal defects than the second nitride semiconductor. For example, the final surface vicinity is 1 × 10 5.^Five/cm²A substrate having the following crystal defects is obtained.
[0028]
During the growth of the third nitride semiconductor layer, the aforementioned n-type impurities such as Si and Sn can be doped. The n-type impurity concentration is 5 × 10 5 as in the case of the second nitride semiconductor layer.¹⁶/cm^Three~ 5x10^{twenty one}/cm^ThreeRange, preferably 1 × 10¹⁷/cm^Three~ 1x10²⁰/cm^ThreeAnd
[0029]
As a more preferable aspect, when the third nitride semiconductor is doped with an n-type impurity, it is desirable to provide a concentration gradient in the n-type impurity. In particular, it is desirable that the concentration gradient is adjusted so that the n-type impurity concentration decreases as the distance from the dissimilar substrate increases. Since the operation is the same as that of the second nitride semiconductor layer, the description thereof is omitted.
[0030]
The thickness of the third nitride semiconductor layer is desirably 10 μm or more, preferably 50 μm or more, and more preferably 100 μm or more. When the thickness is less than 10 μm, the number of crystal defects tends to be less likely to decrease. Although an upper limit is not specifically limited, It is desirable to set it as 1 mm or less. This is because if the growth is thicker than 1 mm, the entire wafer is warped due to the difference in thermal expansion coefficient between the nitride semiconductor and the heterogeneous substrate, and the third nitride semiconductor layer tends to be difficult to grow with a uniform film thickness. .
[0031]
Next, in the fourth step of the present invention, after the growth of the third nitride semiconductor 3, at least the heterogeneous substrate 1, the underlayer 2, and the protective film 10 are removed. FIG. 5 shows the structure after the second nitride semiconductor layer 3 is also removed. For example, when the second nitride semiconductor layer 2 is grown to a thickness of 20 μm or more, a different substrate, an underlayer, The protective film can be removed to leave the second nitride semiconductor 3 as well. In this way, when the different substrate side is removed and the two main surfaces of the substrate made only of the nitride semiconductor are exposed, crystal defects extending in the longitudinal direction may remain on the original different substrate side. However, on the third nitride semiconductor layer side, there are almost no crystal defects extending in the vertical direction, and the entire crystal defects are, for example, 1 × 10 6.^Five/cm²It is very less with the following. Even if another semiconductor layer is stacked on the third nitride semiconductor layer 4, there is no crystal defect in the vertical direction, and therefore there is no threading dislocation of crystal defects, and a very good semiconductor can be stacked. Therefore, when a nitride semiconductor is used as the substrate, it is desirable that the surface opposite to the surface from which the heterogeneous substrate is removed be the growth surface. There are techniques such as polishing and etching to remove the different types of substrates. However, since different materials are laminated, it is most preferable to remove them by polishing.
[0032]
The nitride semiconductor substrate of the present invention is a nitride semiconductor substrate grown by HVPE and having a first main surface and a second main surface, and the first main surface or the vicinity of the second main surface. 1 × 10 crystal defects^FivePiece / cm²The growth method is not particularly limited and is preferably a substrate obtained by the above-described method. Thus, the crystal defects near the surface are 1 × 10^FivePiece / cm²When an element structure is formed by laminating another nitride semiconductor on the following nitride semiconductor substrate, a long-life element excellent in reliability with no crystal defects inside can be obtained. Especially when a laser device is fabricated, the nitride semiconductor substrate has much better thermal conductivity than conventional sapphire, so when the substrate and heat sink are in contact, the heat dissipation is improved and a long-life laser is realized. it can.
[0033]
As a preferred embodiment, the nitride semiconductor substrate is doped with an n-type impurity, more preferably, the n-type impurity has a concentration gradient in the nitride semiconductor substrate, and most preferably the nitride semiconductor substrate. It is desirable that the n-type impurity concentration decreases as one of the first main surface and the second main surface approaches.
[0034]
【Example】
[Example 1]
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
(First step)
A heterogeneous substrate 1 made of sapphire with a 2-inch φ and C-plane as the main surface is set in a MOVPE reaction vessel, and the temperature is set to 500 ° C., and trimethylgallium (TMG), ammonia (NH_Three) Is used to grow a buffer layer (not shown) made of GaN with a film thickness of 200 Å. After growing the buffer layer, the temperature is set to 1050 ° C., and the underlayer 2 made of GaN is grown to a thickness of 4 μm.
[0035]
After the underlayer 2 is grown, the wafer is taken out of the reaction vessel, a striped photomask is formed on the surface of this underlayer, and a SiO 2 having a stripe width of 10 μm and a stripe interval (window) of 2 μm is formed by a CVD apparatus.₂A protective film 10 is formed to a thickness of 0.5 μm. The structure of the wafer after forming the protective film is shown in FIG.
[0036]
(Second step)
After forming the protective film 10, the wafer is set again in the MOVPE reaction vessel, the temperature is set to 1050 ° C., ammonia is 0.27 mol / min, and TMG is 225 μmol / min (V / III ratio = 1200) from undoped GaN. A second nitride semiconductor layer 3 is grown to a thickness of 30 μm. When grown at such a molar ratio, as shown in FIG. 2, the second nitride semiconductor 3 can be grown with the end face being substantially perpendicular to the horizontal surface of the protective film, and crystal defects are greatly reduced. The grown second nitride semiconductor layer can be grown with a uniform film thickness as shown in FIG. 3. When the vicinity of the surface is observed with a TEM, crystal defects extending from the window portion are observed in the second nitride semiconductor layer. It stopped on the way, and there was hardly anything appearing on the surface.
[0037]
(Third step)
After the growth of the second nitride semiconductor layer 3, the wafer is transferred to the HVPE apparatus, and the third nitride semiconductor layer 4 made of undoped GaN is grown to a thickness of 200 μm using Ga metal, HCl gas, and ammonia as raw materials. Let The structure of the grown wafer is shown in FIG. When the number of crystal defects near the surface of the third nitride semiconductor layer after the growth is observed by TEM, 1 × 10^FourPiece / cm²It turned out that the following and the very favorable board | substrate were obtained. Furthermore, even with very few crystal defects, only crystal defects that were almost horizontal to the plane remained.
[0038]
(Fourth process)
Next, the wafer is transferred to a polishing apparatus, and the heterogeneous substrate 1, the underlayer 2, the protective film 10, and the second nitride semiconductor layer 3 are removed using a diamond polishing agent, and the third substrate as shown in FIG. The back surface of the nitride semiconductor layer 4 is exposed to form a nitride semiconductor substrate having a total film thickness of 195 μm. The crystal defects on the back side are also 1 × 10^FivePiece / cm²There were few less.
[0039]
[Example 2]
In the third step of Example 1, silane gas is added to the source gas of HVPE, and Si is first added to 1 × 10.¹⁹/cm^ThreeAs GaN is grown while doping, the flow rate of the silane gas is decreased as the growth proceeds, and finally Si is increased to 5 × 10 5.¹⁶/cm^ThreeAs doped GaN, GaN having a Si concentration gradient is grown to a thickness of 200 μm. Other than that, a nitride semiconductor substrate was obtained in the same manner as in Example 1. As a result, a nitride semiconductor substrate having substantially the same number of crystal defects as that of Example 1 on the surface with a small amount of Si was obtained.
[0040]
[Example 3]
In the second step of Example 1, silane gas is added to the MOVPE source gas, and Si is first added to 1 × 10 6.¹⁹/cm^ThreeAs GaN is grown while doping, the flow rate of silane gas is reduced as the growth proceeds, and finally Si is added at 1 × 10.¹⁷/cm^ThreeAs doped GaN, GaN having a Si concentration gradient is grown to a thickness of 20 μm. Subsequently, in the third step, Si is 1 × 10¹⁷/cm^ThreeDoped GaN is grown to a thickness of 200 μm. Thereafter, in the fourth step, the heterogeneous substrate, the underlayer, the protective film, and the first nitride semiconductor layer are removed by 15 μm. In the nitride semiconductor substrate obtained as described above, the main surface of the third nitride semiconductor layer was almost the same as in Example 1, but the crystal defects on the second nitride semiconductor side were the third. Compared to the nitride semiconductors of this, it was about an order of magnitude more.
[0041]
[Example 4]
The main surface of the nitride semiconductor substrate of Example 1 on the side where the heterogeneous substrate is not removed is faced up, and a nitride semiconductor layer is grown on this surface as follows to obtain the laser device shown in FIG.
[0042]
On the nitride semiconductor substrate 4 obtained in Example 1
(N-side contact layer 21)
Using ammonia and TMG, silane gas as impurity gas, Si was 3 × 10 at 1050 ° C.¹⁸/cm^ThreeAn n-side contact layer 5 made of doped GaN is grown to a thickness of 4 μm.
[0043]
(Crack prevention layer 22)
Next, using TMG, TMI (trimethylindium), and ammonia, the temperature is set to 800 ° C. and In_0.06Ga_0.94A crack prevention layer 22 made of N is grown to a thickness of 0.15 μm. This crack prevention layer can be omitted.
[0044]
(N-side cladding layer 23)
Subsequently, using TMA, TMG and ammonia at 1050 ° C., undoped Al_0.16Ga_0.84A layer made of N is grown to a film thickness of 25 Å, then TMA is stopped, silane gas is flowed, and Si is 1 × 10 × 10.¹⁹/cm^ThreeA layer made of doped n-type GaN is grown to a thickness of 25 Å. These layers are alternately stacked to form a superlattice layer, and an n-side cladding layer 23 made of a superlattice having a total film thickness of 1.2 μm is grown.
[0045]
(N-side light guide layer 24)
Subsequently, the silane gas is stopped, and an n-side light guide layer 8 made of undoped GaN is grown at 1050 ° C. to a thickness of 0.1 μm. The n-side light guide layer 24 may be doped with n-type impurities.
[0046]
(Active layer 25)
Next, the temperature was set to 800 ° C. and undoped In_0.01Ga_0.95A barrier layer of N is grown to a thickness of 100 Å, and then at the same temperature, undoped In_0.2Ga_0.8A well layer made of N is grown to a thickness of 40 Å. A barrier layer and a well layer are alternately stacked three times, and finally, an active layer of a multiple quantum well structure (MQW) having a total film thickness of 520 Å is grown by ending with the barrier layer. The active layer may be undoped as in this embodiment, or may be doped with n-type impurities and / or p-type impurities. Impurities may be doped into both the well layer and the barrier layer, or one of them may be doped. Furthermore, the stacking order may be from the well layer and end with the well layer, from the well layer and end with the barrier layer, or from the barrier layer and end with the well layer.
[0047]
(P-side cap layer 26)
Next, the temperature was raised to 1050 ° C., TMG, TMA, ammonia, Cp 2 Mg (cyclopentadienyl magnesium) was used, and Mg was 1 × 10²⁰/cm^ThreeDoped p-type Al_0.3Ga_0.7A p-side cap layer 26 made of N is grown to a thickness of 300 angstroms.
[0048]
(P-side light guide layer 27)
Stop Cp2Mg and TMA, Mg 5 × 10¹⁶/cm^ThreeA p-side light guide layer 27 made of doped GaN is grown to a thickness of 0.1 μm.
[0049]
(P-side cladding layer 28)
Next, undoped Al_0.16Ga_0.84A layer of N is grown to a thickness of 25 Å, followed by Mg of 1 × 10¹⁹/cm^ThreeLayers made of doped GaN are grown to a thickness of 25 angstroms and are alternately stacked to grow a p-side cladding layer 28 made of a superlattice layer with a total thickness of 0.6 μm.
[0050]
(P-side contact layer 29)
Finally, Mg is 1 × 10²⁰/cm^ThreeA p-side contact layer 29 made of doped p-type GaN is grown to a thickness of 150 Å.
[0051]
The wafer on which the nitride semiconductor has been grown as described above is taken out of the reaction vessel, and SiO 2 is deposited on the surface of the uppermost p-side contact layer 29.₂A protective film is formed, and SiCl is formed using RIE (reactive ion etching)._FourEtching with gas exposes the surface of the n-side contact layer 21 where the n-electrode is to be formed, as shown in FIG.
[0052]
Next, a mask having a predetermined shape is applied to the uppermost p-side contact layer 29, and the p-side contact layer 29 and the p-side cladding layer 28 are etched to form a ridge stripe having a width of 1 μm. ZrO on the side₂An insulating film 30 is formed, and a p-electrode 31 electrically connected to the p-side contact layer is formed through the insulating film 30. On the other hand, an n-electrode 32 is formed on the surface of the n-side contact layer exposed earlier.
[0053]
As described above, the nitride semiconductor substrate of the wafer on which the n-electrode and the p-electrode are formed is polished and thinned, and then the nitride semiconductor substrate is cleaved to form the resonance surface of the laser element on the cleaved surface. After cleavage, it was separated into chips, and the nitride semiconductor substrate side was placed on a heat sink to form a laser element, which showed laser oscillation at room temperature and had a threshold current density of 1.5 kA / cm.²At room temperature, continuous oscillation was observed, and a lifetime of 1000 hours or longer was exhibited at an output of 20 mW.
[0054]
In this example, the laser element was manufactured using the substrate obtained in Example 1. However, even in the case where both the n and p electrodes are extracted from the same surface side, Example 2 and Example 3 are used. A nitride semiconductor substrate in which a concentration gradient is provided in the n-type impurity obtained in (1) can be used. In this case, the n-side contact layer 21 is not necessary, and the second nitride semiconductor layer 3 or the third nitride semiconductor layer provided with a concentration gradient by etching is exposed, and an n-electrode 32 is formed on the exposed surface. That's fine.
[0055]
[Example 5]
On the nitride semiconductor substrate obtained in Example 2 (surface opposite to the surface from which the different substrate is removed), the crack prevention layer 22, the n-side cladding layer 23, and the n-side light guide layer are formed in the same manner as in Example 4. 24, an active layer 25, a p-side cap layer 26, a p-side light guide layer 27, a p-side cladding layer 28, and a p-side contact layer 29 are laminated.
[0056]
Subsequently, a ridge stripe having a width of 1 μm is formed in the p-side contact layer 29 and the p-side cladding layer in the same manner as in Example 4, and the insulating film 30 is formed. After the formation of the insulating film, the nitride semiconductor substrate provided with the concentration gradient was polished to a thickness capable of cleaving, and then cleaved in the same manner as in Example 4 to obtain a laser element. In Example 5, since the concentration gradient is provided even when the nitride semiconductor substrate is polished, the exposed surface is always a layer doped with n-type impurities at a high concentration in the nitride semiconductor substrate. As shown in FIG. 7, when an n-electrode was formed on the substrate side and a p-electrode was formed on the ridge side to form a laser element, a laser element having substantially the same characteristics as in Example 4 was obtained.
[0057]
【The invention's effect】
As described above, according to the method of the present invention, it is possible to obtain a nitride semiconductor substrate having a very good crystallinity which has not been obtained conventionally. When a nitride semiconductor is grown on the nitride semiconductor substrate, the lattice is perfectly matched, so that an element with very few crystal defects can be obtained. Therefore, even if a laser element used in the severest condition, for example, has a threading dislocation reaching the active layer, a long-life and highly reliable element can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a structure of a nitride semiconductor substrate for explaining a first step of the present invention.
FIG. 2 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate for explaining a second step of the present invention.
FIG. 3 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate for explaining a second step of the present invention.
FIG. 4 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate for explaining a third step of the present invention.
FIG. 5 is a schematic cross-sectional view showing the structure of a nitride semiconductor substrate for explaining a fourth step of the present invention.
FIG. 6 is a schematic cross-sectional view showing the structure of a laser device using a substrate according to an embodiment of the present invention.
FIG. 7 is a schematic cross-sectional view showing the structure of a laser device using a substrate according to another embodiment of the present invention.
[Explanation of symbols]
1 ... Different substrates
2 ... Underlayer
3 ... Second nitride semiconductor layer
4 ... Third nitride semiconductor layer
10 ... Protective film
21 ... n-side contact layer
22 ... Crack prevention layer
23 ... n-side cladding layer
24 ... n-side light guide layer
25 ... Active layer
26 ... p-side cap layer
27 ... p-side light guide layer
28 ... p-side cladding layer
29 ... p-side contact layer
30 ... Insulating film
31 ... p electrode
32 ... n electrode

Claims (9)

A base layer made of a first nitride semiconductor is first grown on a different substrate made of a material different from that of the nitride semiconductor, and the nitride semiconductor does not grow on the surface or is difficult to grow on the base layer. a first step of the protective film partially formed with, after the first step, by metalorganic vapor phase epitaxy, the base layer up to the said protective film upper, by growing a second nitride semiconductor A second step of forming a cavity in the substantially central portion of the protective film; and after the second step, the second nitride semiconductor is formed on the second nitride semiconductor layer by hydride vapor phase epitaxy. And a third step of growing a third nitride semiconductor with a thickness greater than that of the layer. 2. The method of manufacturing a nitride semiconductor substrate according to claim 1, wherein the nitride semiconductor is doped with an n-type impurity in at least one of the second step and the third step. 2. The method of manufacturing a nitride semiconductor substrate according to claim 1, wherein the second nitride semiconductor layer is grown in a shape in which an end face is substantially perpendicular to a horizontal plane of the protective film. 2. The nitride semiconductor substrate according to claim 1, wherein the second nitride semiconductor layer is grown by adjusting a molar ratio of a nitrogen source gas (nitrogen source / group 3 source) to 2000 or less. Production method.  3. The nitride semiconductor substrate according to claim 2, wherein a concentration gradient is provided in the n-type impurity in the nitride semiconductor layer in at least one of the second step and the third step. Manufacturing method. 4. The method for manufacturing a nitride semiconductor substrate according to claim 3, wherein the concentration gradient is adjusted such that the n-type impurity concentration decreases as the distance from the different substrate increases. After the third nitride semiconductor growth, at least a heterologous substrate, underlayer, and according to any one of claims 1 to 6, characterized by comprising a fourth step of removing the protective film A method for manufacturing a nitride semiconductor substrate. A nitride semiconductor substrate grown by a hydride vapor phase growth method and having a first main surface and a second main surface, wherein crystal defects near the first main surface or the second main surface are 1 × Ri 10 ⁵ / cm ² or less der, wherein the nitride semiconductor substrate are contained in n-type impurity, the n-type impurity is characterized Rukoto to have a concentration gradient in the nitride semiconductor substrate Nitride semiconductor substrate. 9. The n-type impurity concentration is made smaller as approaching either one of the first main surface and the second main surface of the nitride semiconductor substrate. Nitride semiconductor substrate.

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